Hi,
BCD and ECF are opposite angles and so are equal. If they are equal, then their equations are equal, and if their equations are equal, you can set the equations against each other to find x. See below, and hope this helps!
(10x - 20)° = (8x + 4)°
This is basic algebra. (I'm taking off the degree sign for now to make it simpler, but be sure to add it to your answer at the end.) Group like terms.
10x - 20 = 8x + 4
2x = -16
x = -8
Once you've found "x", plug "x" into the equation for BCD and solve. I'll get you started:
(10 × -8) - 20
